The present invention relates to a technique for driving a motor, and more particularly to a technique for driving a PWM-controlled motor.
U.S. patent application Ser. No. 10/307,986 (filed Dec. 3, 2002) by the same inventors as the present application discloses a motor driving device, which is an example of a technique for driving a motor by energizing motor coils of different phases with PWM control in parallel. A motor driving device of FIG. 13, which is one embodiment disclosed in the application, will now be described.
The motor driving device of FIG. 13 drives a three-phase motor (having U phase, V phase and W phase) by energizing the motor coils with PWM control. This motor driving device includes a plurality of transistors Tr11, Tr12, Tr21, Tr22, Tr31 and Tr32 (hereinafter referred to collectively as xe2x80x9cTrxe2x80x9d) to be switched for appropriately energizing the motor coils, a plurality of diodes D11, D12, D21, D22, D31, D32 (hereinafter referred to collectively as xe2x80x9cDxe2x80x9d) for supplying a regenerative current to the motor coils when the transistors Tr are OFF, a power supply 1 for driving the motor, a Hall signal processing section 2 for producing signals that indicate the rotor position from signals from Hall elements, an energization switching section 3 for switching energized phases at a predetermined cycle, a level shift section 4 for applying the gate voltage of each transistor Tr according to the output from the energization switching section 3, an oscillation section 5 for producing set pulse signals SP1 and SP2, a torque command signal generation section 6 for producing torque command signals TQ1, TQ2 and TQ3 from an original torque command signal TQ, a comparison section 7 for comparing a current detection signal DS with the torque command signals TQ1 to TQ3 to output comparison results CR1, CR2 and CR3, respectively, a masking section 8 for selectively masking or not masking the comparison results CR1 and CR2, and a PWM control section 9 for producing PWM control signals P1 and P2. Note that the current detection signal DS is a signal obtained by amplifying, with an amplifier A, a voltage that is present across the current detection resistor R when the current applied to the motor coil is allowed to flow through the current detection resistor R.
The energization switching section 3 switches the energized phases at a cycle of a period corresponding to 60 electrical degrees in a cycle of a phase current. At the switching, two phases are selected as the energized phases to be energized with PWM control. The remaining one phase is controlled so that the corresponding transistor Tr is fixed to ON for one cycle.
The masking section 8 receives the comparison results CR1 to CR3 from the comparison section 7 and the PWM control signals P1 and P2 from the PWM control section 9 for selectively masking or not masking the comparison results CR1 and CR2 according to the PWM control signals P1 and P2 and the comparison result CR3.
The PWM control section 9 turns ON the PWM control signal P1 according to the set pulse signal SP1, and turns it OFF when detecting, from the comparison result CR1, that the level of the current detection signal DS has reached that of the torque command signal TQ1. Similarly, the PWM control signal P2 is turned ON according to the set pulse signal SP2, and is turned OFF when the PWM control section 9 detects, from the comparison result CR2, that the level of the current detection signal DS has reached that of the torque command signal TQ2.
The operation of the motor driving device of FIG. 13 having such a configuration will now be described with reference to the drawings.
FIG. 14A to FIG. 14C each illustrate a phase current to be applied to a motor coil by the motor driving device of FIG. 13, wherein FIG. 14A illustrates a U-phase current, FIG. 14B illustrates a V-phase current, and FIG. 14C illustrates a W-phase current. Note that each hatched portion in the figures denotes an energized phase to be energized with PWM control, and any other portion denotes an energized phase to be energized while the transistor Tr is fixed to ON.
These phase currents are applied for every 60 electrical degrees according to the torque command signals TQ1 to TQ3 illustrated in FIG. 14D. During a period of 60 electrical degrees, the torque command signal TQ1 keeps increasing, and the torque command signal TQ2 keeps decreasing, with the torque command signal TQ3 being obtained by synthesizing the torque command signal TQ1 with the torque command signal TQ2.
As the energization switching section 3 switches the energized phases at a cycle of a period corresponding to 60 electrical degrees in a cycle of a phase current, the level of each phase current changes as follows. First, in one cycle, the level increases according to the torque command signal TQ1. In the next cycle, the level stays constant according to the torque command signal TQ3. Then, in the following cycle, the level decreases according to the torque command signal TQ2. Then, after the polarity inverts, the level of each phase current undergoes similar transitions. The motor driving device of FIG. 13 drives the motor by using trapezoidal phase currents as illustrated in FIG. 14A to FIG. 14C.
Next, PWM control with the motor driving device of FIG. 13 will be described with reference to the timing charts of FIG. 15A to FIG. 15E, illustrating a portion of FIG. 14A to FIG. 14D around time t1 in an enlarged manner. FIG. 15A illustrates the set pulse signals SP1 and SP2. FIG. 15B illustrates the PWM control signals P1 and P2. FIG. 15C illustrates the torque command signals TQ1 to TQ3 and the current detection signal DS. FIG. 15D and FIG. 15E illustrate the V-phase current and the W-phase current, respectively.
Upon receiving the set pulse signal SP1, the PWM control section 9 turns ON the PWM control signal P1. Thus, the V-phase current is energized (period A in FIG. 15B to FIG. 15D). Then, upon detecting, from the comparison result CR1, that the level of the current detection signal DS has reached that of the torque command signal TQ1, the PWM control section 9 turns OFF the PWM control signal P1. Thus, a regenerative current flows through the V phase (period Axe2x80x2 in FIG. 15D). Similarly, upon receiving the set pulse signal SP2, the PWM control section 9 turns ON the PWM control signal P2. Thus, the W-phase current is energized (period B in FIG. 15B, FIG. 15C and FIG. 15E). Then, upon detecting, from the comparison result CR2, that the level of the current detection signal DS has reached that of the torque command signal TQ2, the PWM control section 9 turns OFF the PWM control signal P2. Thus, a regenerative current flows through the W phase (period Bxe2x80x2 in FIG. 15E).
When the motor driving device of FIG. 13 is driving the motor at a low torque, the ON periods of the PWM control signals P1 and P2 (period A and period B) do not overlap with each other, and the two phases to be PWM-controlled are controlled fully independently. As a result, it is possible to apply trapezoidal phase currents as illustrated in FIG. 14A to FIG. 14C, thereby suppressing vibrations of the motor and thus reducing noise from the motor.
On the other hand, when the motor driving device of FIG. 13 drives the motor at a high torque, the ON periods of the PWM control signals P1 and P2 (period A and period B) overlap with each other.
Next, PWM control when the motor driving device of FIG. 13 drives the motor at a high torque will be described with reference to the timing charts of FIG. 16A to FIG. 16E, illustrating a portion of FIG. 14A to FIG. 14D around time t1 in an enlarged manner. FIG. 16A illustrates the set pulse signals SP1 and SP2. FIG. 16B illustrates the PWM control signals P1 and P2. FIG. 16C illustrates the torque command signals TQ1 to TQ3 and the current detection signal DS. FIG. 16D and FIG. 16E illustrate the V-phase current and the W-phase current, respectively.
Where the ON periods of the PWM control signals P1 and P2 overlap with each other, two phases, i.e., the V phase and the W phase, are energized simultaneously. As a result, the current detection signal DS represents the total amount of current for the two phases being energized simultaneously, as illustrated in FIG. 16C, and the torque command signals TQ1 and TQ2 are no longer proper references for comparison. Therefore, the masking section 8 masks the comparison results CR1 and CR2 so that the PWM control section 9 ignores the comparison results CR1 and CR2 during a period in which the PWM control signals P1 and P2 are both ON. Then, the comparison result CR3 is monitored, and upon detecting, from the comparison result CR3, that the level of the current detection signal DS has reached that of the torque command signal TQ3, either one of the comparison results CR1 and CR2 (the comparison result CR2 in FIG. 16A to FIG. 16E) is unmasked. As a result, either one of the PWM control signals P1 and P2 (the PWM control signal P2 in FIG. 16A to FIG. 16E) is turned OFF by the PWM control section 9, thereby terminating the two-phase simultaneous energization.
Thus, by using the torque command signal TQ3 obtained by synthesizing the torque command signal TQ1 with the torque command signal TQ2, even if two phases to be PWM-controlled are energized simultaneously during a high-torque driving operation of the motor, the two phases can be controlled substantially independently. As a result, energization can be done with trapezoidal waves according to the two torque command signals TQ1 and TQ2, respectively. In this way, even in a high-torque driving operation, it is possible to suppress vibrations of the motor and to reduce noise from the motor.
In the motor driving device of FIG. 13, two phases may not always be energized simultaneously. For example, consider a case where a phase is energized while aiming at the torque command signal TQ1, after the PWM control signal P1 is turned ON. In such a case, if the PWM control section 9 receives the set pulse signal SP2, the PWM control signal P2 is supposed to be turned ON to initiate two-phase simultaneous energization. If, however, the level of the current detection signal DS has increased above the level of the torque command signal TQ2 by the previous energization aiming at the torque command signal TQ1, the PWM control section 9 will not turn ON the PWM control signal P2 based on the comparison result CR2. In such a case, the motor driving device of FIG. 13 fails to energize two phases simultaneously. Therefore, a sufficient electric power cannot be supplied to the motor, thereby resulting in an insufficient torque in the motor, particularly during a high-torque driving operation.
Conversely, if the level of the current detection signal DS does not quickly reach the level of the torque command signal TQ3 in two-phase simultaneous energization, the two-phase simultaneous energization continues for a long period of time. During two-phase simultaneous energization, the energization is performed, aiming not at the individual torque command signals TQ1 and TQ2, but at the total thereof, i.e., the torque command signal TQ3. Therefore, two-phase simultaneous energization continuing for a long period of time not only results in the loss of the parallelism and the independence of the two phases being energized, but also results in the energization of an abnormal phase current.
FIG. 17A to FIG. 17D illustrate how an abnormal phase current occurs when two-phase simultaneous energization continues for a long period of time. FIG. 17A illustrates the set pulse signals SP1 and SP2. FIG. 17B illustrates the current detection signal DS and the torque command signals TQ1 to TQ3. FIG. 17C illustrates a phase current to be energized according to the torque command signal TQ1, and FIG. 17D illustrates a phase current to be energized according to the torque command signal TQ2.
FIG. 17B illustrates a case where after two-phase simultaneous energization is initiated, the level of the current detection signal DS representing the total amount of current does not reach the torque command signal TQ3, whereby the two-phase simultaneous energization continues over a number of cycles of the set pulse signals SP1 and SP2. In such a case, currents that are substantially deviated from the torque command signals TQ1 and TQ2 flow through the energized phases, as illustrated in FIG. 17C and FIG. 17D. If two-phase simultaneous energization continues for a long period of time, the parallelism and the independence of the two phases being energized according to the two PWM control signals P1 and P2 are lost, thereby failing to apply trapezoidal phase currents. This results in vibrations of the motor and noise from the motor.
Furthermore, in the motor driving device of FIG. 13, the timing at which the PWM control signal P1 or P2 is turned ON by the PWM control section 9 may not coincide with the timing at which the energization switching section 3 switches the energized phases, i.e., the start of a block corresponding to 60 electrical degrees in a cycle of a phase current (hereinafter referred to as xe2x80x9cblock starting pointxe2x80x9d). In such a case, a distortion may occur in a phase current, or an erroneous phase current may be energized.
FIG. 18A to FIG. 18E are timing charts illustrating a portion of FIG. 14A to FIG. 14D around time t2 in an enlarged manner. Note that time t2 is a block starting point at which energized phases are switched by the energization switching section 3. FIG. 18A illustrates the set pulse signals SP1 and SP2. FIG. 18B illustrates the current detection signal DS and the torque command signals TQ1 to TQ3. FIG. 18C, FIG. 18D and FIG. 18E illustrate the U-phase current, the V-phase current and the W-phase current, respectively.
In FIG. 18A to FIG. 18E, before time t2, the U-phase current is the total current of the V-phase current and the W-phase current, the V-phase current is energized while aiming at the torque command signal TQ1, and the W-phase current is energized while aiming at the torque command signal TQ2. Then, after time t2, the U-phase current is energized while aiming at the torque command signal TQ2, the V-phase current is the total current of the U-phase current and the W-phase current, and the W-phase current is energized while aiming at the torque command signal TQ1.
As illustrated in FIG. 18A to FIG. 18E, if the block starting point does not coincide with the set pulse signal SP1 or SP2, a new energized phase cannot be energized until a new set pulse signal SP1 or SP2 is received after the start of a new block of 60 electrical degrees. Therefore, the period for which a regenerative current flows increases, thereby resulting in a distortion in a phase current as indicated by arrows in FIG. 18C and FIG. 18D. Moreover, even after the energized phases are switched, the energized state of the previous cycle remains, whereby an erroneous energized phase may be energized. These factors may result in vibrations of the motor or noise from the motor.
The present invention has been made in view of the above, and has an object to further suppress vibrations of a motor and to reduce noise from the motor while giving a sufficient torque to the motor, with a motor driving device as illustrated in FIG. 13, for example. More specifically, it is an object of the present invention to ensure that two phases are energized simultaneously during a high-torque driving operation of the motor, while avoiding two-phase simultaneous energization continuing for a long period of time. It is also an object of the present invention to eliminate a distortion in a phase current due to a shift between a block starting point and the start of energization.
In order to achieve the object set forth above, the present invention provides a motor driving device for driving a motor by energizing motor coils with PWM control, the motor driving device including: an energization switching section for determining a first energized phase and a second energized phase to be PWM-controlled, the determination being made at a predetermined cycle; a torque command signal generation section that receives an original torque command signal for producing a first torque command signal and a second torque command signal each having an amplitude according to the original torque command signal, and also producing a third torque command signal, which is obtained by synthesizing the first and second torque command signals together; a comparison section that receives the first to third torque command signals and a current detection signal, which is obtained by detecting a current being supplied to the motor, for comparing the current detection signal with the first to third torque command signals to output a first comparison result, a second comparison result, and a third comparison result, respectively; an oscillation section for producing a first set pulse signal and a second set pulse signal; a PWM control section that receives the first and second set pulse signals and the first and second comparison results for producing a first PWM control signal that is turned ON according to the first set pulse signal and turned OFF according to the first comparison result, and also producing a second PWM control signal that is turned ON according to the second set pulse signal and turned OFF according to the second comparison result; and a masking section that receives the first and second PWM control signals and the first to third comparison results for selectively masking or not masking the first and second comparison results according to the first and second PWM control signals and the third comparison result, wherein: the masking section receives the first and second set pulse signals so as to mask the first comparison result according to the first set pulse signal and mask the second comparison result according to the second set pulse signal; and the motor driving device energizes the first and second energized phases with PWM control in parallel according respectively to the first and second PWM control signals.
With the motor driving device of the present invention, in a case where the first (or second) energized phase is energized according to the first (or second) PWM control signal, when the PWM control section receives the second (or first) set pulse signal, the second (or first) comparison result is masked by the masking section so as to be invalidated, whereby even if the level of the current detection signal at this point is equal to or greater than that of the second (or first) torque command signal, the PWM control section can reliably turn ON the second (or first) PWM control signal, without being influenced by the second (or first) comparison result. Therefore, in addition to the first (or second) phase current, the second (or first) phase current can be energized.
The present invention provides another motor driving device for driving a motor by energizing motor coils with PWM control, the motor driving device including: an energization switching section for determining a first energized phase and a second energized phase to be PWM-controlled, the determination being made at a predetermined cycle; a torque command signal generation section that receives an original torque command signal for producing a first torque command signal and a second torque command signal each having an amplitude according to the original torque command signal, and also producing a third torque command signal, which is obtained by synthesizing the first and second torque command signals together; a comparison section that receives the first to third torque command signals and a current detection signal, which is obtained by detecting a current being supplied to the motor, for comparing the current detection signal with the first to third torque command signals to output a first comparison result, a second comparison result, and a third comparison result, respectively; an oscillation section for producing a first set pulse signal and a second set pulse signal; a PWM control section that receives the first and second set pulse signals and the first and second comparison results for producing a first PWM control signal that is turned ON according to the first set pulse signal and turned OFF according to the first comparison result, and also producing a second PWM control signal that is turned ON according to the second set pulse signal and turned OFF according to the second comparison result; and a masking section that receives the first and second PWM control signals and the first to third comparison results for selectively masking or not masking the first and second comparison results according to the first and second PWM control signals and the third comparison result, wherein: the PWM control section receives a first reset pulse signal and a second reset pulse signal, which are externally provided or internally produced, for turning OFF the first PWM control signal according to the first reset pulse signal and turning OFF the second PWM control signal according to the second reset pulse signal; and the motor driving device energizes the first and second energized phases with PWM control in parallel according respectively to the first and second PWM control signals.
With the motor driving device of the present invention, the PWM control section unconditionally turns OFF the first (or second) PWM control signal according to the first (or second) reset pulse signal, whereby the energization of the first (or second) energized phase can be discontinued unconditionally. Thus, it is possible to avoid a situation where two-phase simultaneous energization continues for a long period of time.
It is preferred that: the masking section masks the first and second comparison results during a period in which the first and second PWM control signals are both ON; and during said period, the second comparison result is kept masked for a predetermined period of time and then unmasked according to the first reset pulse signal, and the first comparison result is kept masked for a predetermined period of time and then unmasked according to the second reset pulse signal.
In this way, while the first and second PWM control signals are both ON, i.e., during two-phase simultaneous energization, the PWM control section unconditionally turns OFF the first (or second) PWM control signal, and the masking section unmasks the first (or second) comparison result, according to the first (or second) reset pulse signal, whereby it is possible to erroneously turn OFF also the second (or first) PWM control signal when terminating the two-phase simultaneous energization.
Immediately after the first (or second) PWM control signal is turned OFF during two-phase simultaneous energization, the current detection signal may temporarily indicate a level as high as that during two-phase simultaneous energization, and the level of the current detection signal may have already reached that of the second torque command signal. In view of this, the second (or first) comparison result is kept masked until the current detection signal settles to a proper level after the first (or second) PWM control signal is turned OFF according to the first (or second) reset pulse signal, thereby preventing the second (or first) PWM control signal from being turned OFF erroneously.
The present invention provides another motor driving device for driving a motor by energizing motor coils with PWM control, the motor driving device including: an energization switching section for determining a first energized phase and a second energized phase to be PWM-controlled, the determination being made at a predetermined cycle; a torque command signal generation section that receives an original torque command signal for producing a first torque command signal and a second torque command signal each having an amplitude according to the original torque command signal; a comparison section that receives the first and second torque command signals and a current detection signal, which is obtained by detecting a current being supplied to the motor, for comparing the current detection signal with the first and second torque command signals to output a first comparison result and a second comparison result, respectively; an oscillation section for producing a first set pulse signal and a second set pulse signal; and a PWM control section that receives the first and second set pulse signals and the first and second comparison results for producing a first PWM control signal that is turned ON according to the first set pulse signal and turned OFF according to the first comparison result, and also producing a second PWM control signal that is turned ON according to the second set pulse signal and turned OFF according to the second comparison result, wherein the first and second energized phases are energized with PWM control in parallel according respectively to the first and second PWM control signals so that a start of the predetermined cycle coincides with a timing at which the first or second PWM control signal is turned ON.
With the motor driving device of the present invention, the start of the predetermined cycle, at which the energization switching section is operated, i.e., the timing at which new first and second energized phases are determined, coincides with the timing at which the first or second PWM control signal is turned ON, whereby energization of the first or second energized phase can be started quickly after the first and second energized phases are determined by the energization switching section. Thus, it is possible to eliminate a distortion in a phase current due to a delay in the initiation of the energization at the start of the predetermined cycle, at which the energization switching section is operated, and to prevent an erroneous energized phase from being energized.
It is preferred that the energization switching section receives the first or second set pulse signal for making the start of the predetermined cycle coincide with a timing at which the first or second set pulse signal is turned ON.
It is preferred that: the energization switching section produces a signal indicating a start of the predetermined cycle; and the PWM control section receives the signal indicating the start of the predetermined cycle for turning ON the first or second PWM control signal according to the signal indicating the start of the predetermined cycle.
In order to achieve the object set forth above, the present invention provides a motor driving method for driving a motor by energizing motor coils with PWM control, the motor driving method including: an energization switching step of determining a first energized phase and a second energized phase to be PWM-controlled, the determination being made at a predetermined cycle; a torque command signal generation step of producing a first torque command signal and a second torque command signal each having an amplitude according to a given original torque command signal, and also producing a third torque command signal, which is obtained by synthesizing the first and second torque command signals together; a comparison step of comparing a current detection signal, which is obtained by detecting a current being supplied to the motor, with the first to third torque command signals; a PWM control step of producing a first PWM control signal and a second PWM control signal according to a given first set pulse signal, a given second set pulse signal and comparison results from the comparison step; and a masking step of selectively masking or not masking the comparison results based on the first and second PWM control signals and the comparison result from the comparison step, wherein: the PWM control step uses a given first reset pulse signal and a given second reset pulse signal for turning OFF the first PWM control signal according to the first reset pulse signal and turning OFF the second PWM control signal according to the second reset pulse signal; and the motor driving method energizes the first and second energized phases with PWM control in parallel according respectively to the first and second PWM control signals.
The present invention provides another motor driving method for driving a motor by energizing motor coils with PWM control, the motor driving method including: an energization switching step of determining a first energized phase and a second energized phase to be PWM-controlled, the determination being made at a predetermined cycle; a torque command signal generation step of producing a first torque command signal and a second torque command signal each having an amplitude according to a given original torque command signal; a comparison step of comparing a current detection signal, which is obtained by detecting a current being supplied to the motor, with the first and second torque command signals; and a PWM control step of producing a first PWM control signal and a second PWM control signal according to a given first set pulse signal, a given second set pulse signal and comparison results from the comparison step, wherein the first and second energized phases are energized with PWM control in parallel according respectively to the first and second PWM control signals so that a start of the predetermined cycle coincides with a timing at which the first or second PWM control signal is turned ON.